Preparation of crystalline sulfides and selenides of cadmium zinc and mercury

ABSTRACT

Well-ordered hexagonal crystalline forms of the sulfides, selenides or solid solutions of the sulfides and selenides of cadmium, zinc or mercury are produced by treating crude, amorphous precipitates of the sulfides, selenides or mixtures of sulfides and selenides with aqueous ammonium sulfide. The crystalline cadmium sulfide-containing precipitates are particularly useful as pigments.

United States Patent [1 1 Daly Dec. 3,1974

[ PREPARATION OF CRYSTALLINE SULFIDES AND SELENIDES OF CADMIUM ZINC ANDMERCURY James Ernest Daly, Hudson Falls, NY.

Hercules Incorporated, Wilmington, Del.

Filed: Oct. 24, 1972 Appl. No.: 300,028

Inventor:

Assignee:

References Cited FOREIGN PATENTS OR APPLICATIONS 2/1963 Great Britain423/509 OTHER PUBLICATIONS Mellor: A Comprehensive Treatise on Inorganic& Theoretical Chemistry, Vol. 4, (1923), p. 588.

Allen and Crenshaw: Sulfides of Zinc, American Journal of Science,Series 34, 341-396 (1912).

Primary Examiner-Oscar R. Vertiz Assistant ExaminerHoke S. MillerAttorney, Agent, or Firm-l-Iazel L. Deming [5 7 ABSTRACT Well-orderedhexagonal crystalline forms of the sulfides, selenides or solidsolutions of the sulfides and selenides of cadmium, zinc or mercury areproduced by treating crude, amorphous precipitates of the sulfides,selenides or mixtures of sulfides and selenides with aqueous ammoniumsulfide. The crystalline cadmium sulfide-containing precipitates areparticularly useful as pigments.

6 Claims, N0 Drawings PREPARATION OF CRYSTALLINE SULFIDES AND SELENIDESOF CADMIUM ZINC AND MERCURY This invention relates to production ofcrystalline compounds from Group IIB and sulfur and/or selenium, andmore particularly to a process for converting crude cadmiumsulfide-containing precipitates into pigmentary grade materials.

Various methods have been proposed for converting crude cadmiumsulfide-containing precipitates into pigments. One method involvesheating the crude, usually in a non-oxidizing atmosphere, at elevatedtemperatures of about 400 to 700 C. (the so-called calcinationtreatment). Another method concerns heating the crude under pressure inaqueous medium in the presence of a small quantity of analkaline-reacting salt at elevated temperatures and preferably at about360 C. Still another method relates to heating an aqueous slurry ofcrude cadmium sulfo-selenide in the presence of 1,000 to 2,000 percentof an alkali metal hydroxide and 50 to 150 percent of an alkali oralkaline earth metal nitrate, sulfate, halide or aluminate at 90 to 160C. It has also been proposed to purify compounds of Groups [l8 and VlAby heating the compounds in a water slurry of an alkaline earth halidein a flow of inert gas in a furnace at about l,000 C. until theimpurities have reacted with the halide and been removed by the gas.These prior art treatments require high tempera tures, high temperaturesand pressures or large amounts of alkali to promote the crystal growthand particle size development necessary for a good pigment. Thus, anyadvantages in lower processing conditions are offset by the highinvestments required for equipment, maintenance and recovery ofchemicals.

Now, in accordance with the present invention, it has been found thatcrude amorphous precipitates of the sulfides, selenides or mixtures ofthe sulfides and selenides of cadmium, zinc, or mercury can be refinedwithout the prior art disadvantages to give crystalline products whichare of particular value as pigments for coloring materials in huesranging from light yellow through the oranges to reds.

Accordingly, the present invention relates to a process for producingcrystalline sulfides, selenides or solid solutions of sulfides andselenides of cadmium, zinc or mercury, which process comprises treatinga crude, essentially amorphous precipitate of at least one sulfide,selenide or mixture of sulfides and selenides of cadmium, zinc ormercury with sufficient of an aqueous ammonium sulfide solution toprovide a weight ratio of solution to precipitate of at least 1:] and aweight ratio of ammonium sulfide to precipitate of at least 0.02:1 untilthe precipitate is converted to the well-ordered hexagonal crystallinestate, and then recovering the crystalline product so produced.

The process of the invention have been found to be applicable to anyGroup "B sulfide, selenide or mixture of sulfides and selenides and isof particular value when applied to the cadmium sulfide-containingprecipitates. For example, the invention is particularly useful forrefining cadmium sulfide, mixtures of cadmium sulfide and cadmiumselenide, mixtures of cadmium sulfide and zinc sulfide and mixtures ofcadmium sulfide and mercury sulfide. The invention is also useful foraging the pure cadmium pigments as well as the extended pigments such asthose of the so-,called lithopone type.

The crude, essentially amorphous precipitates which are treated inaccordance with the invention can be prepared by any of the knownmethods for producing the desired crude precipitates of cadmium, zinc ormercury sulfides, selenides or mixtures of sulfides and selenides, asfor example by reacting aqueous solutions or suspensions of salts ofcadmium, zinc and/or mercury with solutions of an alkali metal oralkaline earth metal sulfide and/or selenide. Typically, the cadmium,zinc or mercury salt is a nitrate, sulfate or halide. By the suitablechoice of raw materials such as cadmium, zinc, mercury, sulfur andselenium, a series of crudes can be produced yielding a wide range ofcolored pigments with hues varying from light yellow through the orangesto the reds and maroons. 7

As stated, the method of the invention is a wet conversion process inwhich crude, amorphous precipitates of at least one sulfide, selenide ormixture of sulfides and selenides of cadmium, zinc or mercury aretreated in the presence of aqueous ammonium sulfide until theprecipitate is converted to the wellordered crystalline state whichexhibits by x-ray diffraction a welldeveloped hexagonal crystalstructure. The treatment can be carried out at any convenienttemperature but will usually be conducted within the range of from about0 C. to about 300 C. and preferably from about 20 C. to about 275 C. forperiods of time ranging from less than about 1 hour up to several daysor more. Longer times, of course, will be required to perfectcrystallization at lower temperatures. Moreover, by the judiciousselection of the conditions of time, temperature and ammonium sulfideconcentration, series of products with varying degrees of transparency,strength and cleanness can be produced.

The amount of ammonium sulfide solution which is used in the practice ofthe invention is an amount sufficient to provide a weight ratio ofsolution to precipitate (dry crude) of at least 1:1 and a weight ratioof ammonium sulfide ((Nl-l S) to precipitate of at least 0.02:1.Preferably the ratio of solution to precipitate will range from 1.521 to20:1 and most preferably from 2:1 to 10:1, and the ratio of ammoniumsulfide to precipitate will range from 0.05:1 to 15:1 and mostpreferably from 0.1:1 to 10:1. The concentration of the ammonium sulfidein the treating solution can vary within relatively wide limits andusually will range from about 2 percent to about percent and preferablyfrom about 5 percent to about 50 percent by weight of solution. Otherammonium salts and particularly such salts as the nitrates, sulfates orhalides can also be present in the treating solution in varying amountsproviding they do not detract from the advantages of the invention. Theamount of such other salts used will usually vary from about 5 percentto about 25 percent by weight of the treating solution.

The crude precipitate which is treated in accordance with this inventioncan be freshly formed precipitate in the aqueous medium in which it isformed, a filter cake or press cake of the precipitate, or precipitatewhich has been filtered, washed and, if desired, dried and pulverized.

The treatment of the invention does not require agitation, grinding,milling, etc. However, such can be used, if desired, to insure intimatecontact and to facilitate handling.

The products produced in accordance with the invention are crystalline,highly colored materials. The

cadmium sulfide-containing materials in particular are characterized bya broad range of properties exhibiting maxima in transparency, purity ofmasstone and tinctov rial strength and range in color from light yellowthrough oranges to the reds. They can be prepared in all of the desiredhues for commercial pigment applications, as warranted.

The invention will now be illustrated by reference to the followingexamples in which all parts and percentages are by weight unlessotherwise specified.

EXAMPLE VI A crude cadmium sulfide precipitate is prepared by adding 600parts of a 9% aqueous solution of sodium sulfide at 60 C. over a periodof minutes to 480 parts of an agitated, 34.1 percent aqueous solution ofcadmium nitrate maintained at 50 C. Agitation is continued for 1 hour at50 C. after which time the resulting slurry is filtered and theprecipitate is washed to remove soluble salts, dried and pulverized. Thedry crude (100 parts) is next combined with 640 parts of a 9 percentaqueous ammonium sulfide solution in a vessel, the vessel is closed andthe contents are allowed to age for 16 hours at 30C. without agitation,after which time the aged product is recovered from the ammonium sulfideliquor, washed, dried and pulverized. The product is a highlytransparent, golden yellow pigment which exhibits by x-ray diffractionthe hexagonal crystal structure of cadmium sulfide. The product is apigment of good coloring power and gives clean, intense tint tones.

EXAMPLE 2 The procedure of Example 1 is repeated except that in thisexample the washed precipitate (400 parts of pulp containing 100 partsof crude on a dry basis) is not dried or pulverized, but is combinedwith 340 parts of a 17 percent aqueous ammonium sulfide solution in thevessel. The crystalline product of this example is a highly transparent,golden yellow pigment and is substantially identical with the product ofExample 1.

EXAMPLE 3 The procedure of Example l is repeated except that in thisexample the slurry containing the cadmium sul- -fide precipitate iscooled to 30 C. and transferred directly to the vessel withoutfiltration, washing, drying and pulverizing, and, therein, the slurry iscombined with 516 parts of a 24 percent aqueous solution of ammoniumsulfide. The crystalline product is a transparent golden yellow pigmentwhich is substantially identical with the product of Example 1.

EXAMPLE 4 The procedure of Example 1 is repeated except that the vesselcontents are aged for 16 hours at 70 C. The product of this example is agolden yellow pigment similar in hue, but cleaner by reflected light andless transparent than the product of Example 1.

EXAMPLE 5 The procedure of Example 1 is repeated except that the 100parts of dry crude are combined witha solution prepared by dissolving l12 parts of ammonium sulfate and 66 parts of sodium sulfide in 462 partsof water. The crystalline product of this example is a highlytransparent golden yellow pigment which is substantially identical withthe product of Example 1.

EXAMPLE 6 A dry crude cadmium sulfide precipitate is prepared as inExample 1 and the crude (100 parts, dry weight) is pebble milled with640 parts of an 18 percent aqueous solution of ammonium sulfide for 48hours at 30 C., after which time the product is recovered as in Examplel. The crystalline product is a golden yellow pigment which is similarin hue but more opaque than the product of Example 1. The product ofthis example is characterized by unusually high tinctorial strength andcleanness.

EXAMPLE 7 A crude precipitate of a mixture of cadmium sulfide and zincsulfide is prepared by adding 487 parts of an aqueous solutioncontaining 148 parts of cadmium nitrate and 18.6 parts of zinc nitrateat 25 C. over 10 minutes to 500 parts of an agitated aqueous solutioncontaining 58 parts of sodium sulfide maintained at 50 C. Agitation iscontinued for 1 hour at 50 C. after which time the resulting slurry isfiltered and the precipitate is recovered in the manner of Example 1.The dry crude (100 parts) is next combined with 1,140 parts of a 10.5percent aqueous ammonium sulfide solution in a vessel, the vessel isclosed and the contents are aged without agitation for 16 hours at C.,after which time the product is recovered according to the manner ofExample 1. The product is a highly transparent, primrose yellow pigmenthaving high tinctorial strength and clarity. The product exhibits byxray diffraction a hexagonal crystal structure and is a solid solutionof cadmium sulfide and zinc sulfide.

EXAMPLE 8 A crude precipitate of a mixture of cadmium sulfide andmercury sulfide is prepared by adding an aqueous solution previouslyprepared by combining 575 parts of a 9 percent sodium sulfide solutionand 54 parts of a 30 percent mercuric nitrate solution at 60 C. over 10minutes to 1,810 parts of an agitated 8, percent aqueous solution ofcadmium nitrate maintained at 60 C. Agitation is continued for 1 hour at60 C. after which time the crude precipitate is recovered in the mannerof Example l. The dry crude parts) is next combined with 400 parts of a55 percent aqueous solution of ammonium sulfide in a vessel, the vesselsealed and the vessel contents aged for 142 hours at 30 C., after whichtime the aged product is recovered in the manner of Example 1. Theproduct is a highly transparent deep orange pigment having hightinctorial strength. The product exhibits by x-ray diffraction ahexagonal crystal structure and is a solid solution of cadmium sultideand mercury sulfide.

EXAMPLE 9 A crude precipitate of a mixture of cadmium sulfide andcadmium selenide is prepared by adding a solution of sodium sulfide andsodium selenide (previously prepared by dissolving 14 parts of seleniumin 425 parts of a 10.1 percent aqueous solution of sodium sulfide at 60C.) over 10 minutes to an agitated slurry of cadmium carbonate andcadmium nitrate maintained at 50 C., the slurry having been prepared byreacting 430 parts of a 35 percent aqueous solution of cadmium nitratewith 260 parts of a 3.5 percent aqueous solution of sodium carbonate at25 C. Agitation is continued for 1 hour at 50 C., after which timeprecipitate is removed by filtration. The precipitate is washed toremove soluble salts, dried and pulverized. 100 parts of 5 thepulverized crude precipitate is mixed with 500 parts of a 24 percentaqueous solution of ammonium sulfide in a pressure vessel equipped withan agitator, the vessel is sealed and the contents are agitated for 4hours at 250 C. under about 1,000 pounds per square inch pressure, afterwhich time the pressure is released and the product recovered in themanner of Example 1. The product is a medium red pigment exhibiting byx-ray diffraction a hexagonal crystal structure and is a solid solutionof cadmium sulfide and cadmium selenide.

What I claim and desire to protect by Letters Patent is:

1. A process for converting a crude, essentially amorphous precipitateof cadmium sulfide, or a mixture of cadmium sulfide and cadmiumselenide, zinc sulfide 0r mercury sulfide into a pigment having an x-raydiffraction pattern characteristic of the hexagonal crystallinestructure, which process comprises treating said crude,

essentially amorphous precipitate with sufficient of an aqueous solutioncontaining from about 5 percent to about 55 percent by weight ofammonium sulfide to provide a weight ratio of solution to precipitate ofat least 2:1 and a weight ratio of ammonium sulfide to precipitate of 0.1 :1 to 10:1 at a temperature from about 20 C. to about 275 C. for aperiod of time ranging from about 1 to about 6 days until saidprecipitate is converted to the well-ordered hexagonal crystalline stateand recovering the crystalline pigment so produced.

2. The process of claim 1 wherein the pigment is cad-' mium sulfide.

3. The process of claim 1 wherein the pigment is a solid solution ofcadmium sulfide and cadmium selenide.

4. The process of claim 1 wherein the pigment is a solid solution ofcadmium sulfide and zinc sulfide.

5. The process of claim 1 wherein the pigment is a solid solution ofcadmium sulfide and mercury sulfide.

6. The process of claim 1 wherein the recovered crys-

1. A PROCESS FOR CONVERTING A CRUDE, ESSENTIALLY AMORPHOUS PRECIPITATEOF CADMIUM SULFIDE, OR A MIXTURE OF CADMIUM SULFIDE AND CADMIUMSELENIDE, ZINC SULFIDE OR MERCURY SULFIDE INTO A PIGMENT HAVING AN X-RAYDIFFRACTION PATTERN CHARACTERISTIC OF THE HEXAGONAL CRYSTALLINESTRUCTURE, WHICH PROCESS COMPRISES TREATING SAID CRUDE, ESSENTIALLYAMORPHOUS PRECIPITATE WITH SUFFICIENT OF AN AQUEOUS SOLUTION CONTAININGFROM ABOUT 5 PERCENT TO ABOUT 55 PERCENT BY WEIGHT OF AMMONIUM SULFIDETO PROVIDE A WEIGHT RATIO O SOLUTION TO PRECIPATE OF AT LEAST 2:1 AND AWEIGHT RATIO OF AMMONIUM SULFIDE TO PRECIPITATE OF 0.1:1 TO 10:1 AT ATEMPERATURE FROM ABOUT 20*C. TO ABOUT 275* C. FOR A PERIOD OF TIMERANGING FROM ABOUT 1 TO ABOUT 6 DAYS UNTIL SAID PRECIPITATE IS CONVERTEDTO THE WELL-ORDERED HEXAGONAL CRYSTALLINE STATE AND RECOVERING THECRYSTALLINE PIGMENT SO PRODUCED.
 2. The process of claim 1 wherein thepigment is cadmium sulfide.
 3. The process of claim 1 wherein thepigment is a solid solution of cadmium sulfide and cadmium selenide. 4.The process of claim 1 wherein the pigment is a solid solution ofcadmium sulfide and zinc sulfide.
 5. The process of claim 1 wherein thepigment is a solid solution of cadmium sulfide and mercury sulfide. 6.The process of claim 1 wherein the recovered crystalline pigment iswashed, dried and pulverized.